A deep game that will last you months.
I'm a little late to the party. Call of Duty 4 came out almost 2 years ago now, but it is absolutely worth anyone's time if you haven't already dove into its intense campaign and deep multiplayer.
The campaign is short and will take you probably around 5 or 6 hours on a regular difficulty, but the quality of that campaign is great. The game is very scripted and linear, but this didn't bother me too much due to just how much fun it is; and if you're familiar with the Call of Duty series and are even considering buying this one, you probably know about how linear things are already.
The quality of the story is what's most impressive. It might not be all realistic, but it's very intense and you'll feel like you're in an action movie all the way through. There's plenty of dramatic set-pieces and twists in the storyline, especially around the end of the game. The missions can be very challenging, particularly one where you have to wait for a hellicopter to arrive while tons of terrorists come after you. It's never too hard though, unless you play it on the higher difficulty levels. It's very intense, and it's satisfying when you complete a mission.
The missions themselves are pretty varied. There's a sniper mission where you're running around in a ghillie suit stealthily, and a few vehicle sequences as well.
The sound is also very impressive. You'll hear plenty of bullets whizzing by your head, and the weapons feel very real due to the handling and the sounds they make. This game really benefits from some good quality speakers or surround sound, especially considering how cinematic it all is. The graphics are equally as impressive, even by 2009 standards. Textures will look a little bland up close, but the lighting and shadowing is great. You'll especially notice how great the game looks during the later sniper mission.
Like previous Call of Duty games, you'll be aiming down the sight of your gun most of the time. There's plenty of weapons in this game and you can carry two at once, although this isn't like in tactical shooters where you'll be choosing your loadout before each mission. But you're free to pick up any weapon dropped by fallen enemies should you run out of ammo, and all of the weapons here can be useful. There's also a nice melee attack where you rip out a knife and take someone out really fast, which can be very satisfying specially in multiplayer. It's very useful when you get in a bad situation when you're reloading or about to die.
There's a very deep multiplayer component as well. You start off with a few classes to cloose from, such as an assault class, a more stealthy class, and demolitions; and after you warm up a bit in the multiplayer, you'll unlock the ability to create your own classes. You'll be unlocking different weapons, weapon attachments, and weapon camoflauge as you level up in the multiplayer. You'll also be unlocking perks, which helps you customize your character a bit - things like extra bullet penetration that help you shoot through walls, the ability to plant claymores, extra grenades, extra health, and so on. There's also a perk called Martyrdom that lets you drop a live grenade when you die, which is pretty awesome. There's nothing like dying and then seeing everyone run from you to escape the blast of your grenade.
There's plenty of maps and game modes. There's the standard deathmatch and team deathmatch modes, and other modes such as Sabotage which is sort of like in Counter Strike. One team has to pick up and plant a bomb, while the other team tries to keep that from happening. These rounds can go on for quite a while as the bomb will constantly be defused or dropped, which can be very fun. Good teamwork can go a long way here.
You can get kill streaks in the multiplayer as well, which are very useful - if you get a 3 kill streak, you can call in a UAV, which makes everyone on the other team appear on your team's radar. Get a 5 kill streak and you can call in an air strike, and if you get a 7 kill streak you can call in a hellicopter which will go around the map and take out anyone it sees from the other team. This is part of what makes the multiplayer so addicting, it's fun trying to get high kill streaks. Also, in case you're wondering, no, you shouldn't have any problem getting into the multiplayer. There's plenty of skilled people playing this game, but you'll have no trouble adapting to it and you'll quickly be getting some kill streaks - I got a 20 kill streak on my first time playing the game online, and I'm usually not very good playing games online.
There are no online achievements, but there are "challenges", which sort of resemble them. There's weapon challenges, such as "Get 75 kills with an AK-47" or "get 75 headshots", which give you some XP and a weapon attachment or skin when you complete them. If you work towards it, you can even get a golden version of your weapon - which is just what it sounds like. It's a nice, shiny gold version of the weapon.
There's other, more varied challenges, like destroying a certain amount of vehicles or getting a said amount of crouch kills. These might sound a little repetitive, but it does give you something to work towards, so the online component doesn't get stale like it might in old-school shooters.
There are some issues though. There is some very noticeable clipping that becomes a problem in the multiplayer, where your leg might stick out from a wall of a house and someone can snipe you through it. It can be frustrating when this happens, but it's not a big deal.
So all in all, Call of Duty 4 is a fantastic game. The campaign is intense, and although it's short, it's still a very high quality campaign that you'll want to replay more than once.. The online component is deep, and should last anyone a good long time - I've been playing it regularly for 4 months so far. This game is definitely worth your cash, if you don't already own it and you're a fan of shooters.